Hydraulic seamer



Ap 1962 G. E. MUNSCHAUER ETAL 3,030,900

HYDRAULIC SEAMER Filed April 11, 1958 I 6 Sheets-Sheet 1 u Fig.1.

INVENTORS l5 Gaorge EMLmschauQr ATTORNEYS.

April 24, 1962 G. E. MUNSCHAUER ETAL 3,030,900

HYDRAULIC SEAMER Filed April 11, 1958 6 Sheets-Sheet 3 INVENTORS GearefiMzmschauer ATTORNEYS.

April 1962 G. E. MUNSCHAUER ETAL 3,030,900

HYDRAULIC SEAMER Filed April 11, 1958 6 Sheets-Sheet 4 Tim INVENTORSdeorgefiflzmscfzauer. BY ELQJVSPJQ10LL, @MQW MAZQb ATTORNEYS.

April 1962 G. E. MUNSCHAUER ETAL 3,030,900

' HYDRAULIC SEAMER Filed April-ll, 195a s Sheets-Sheet 5 14 76 Flag. 9.137

GQ0rgaEMu g$h Z 51Qr BY @LQIVSPJQfOZl, Calm, @mg QWQ QM ATTORNEYS.

April 1962 G. E. MUNSCHAUER ETAL 3,030,900

HYDRAULIC SEAMER Filed April 11, 1958 6 Sheets-Sheet 6 FiQJO.

IN VENTORS GwrcQE/fumchauer ATTORNEY;

{and

3,030,900 HYDRAULEC SEAMER George E. Munschauer, Eggertsville, and LeivS. Platou, Snyder, N.Y., assignors to Niagara Machine & Tool Works,Buttaio, NDY.

Filed Apr. 11, 1958, Ser. No. 727,983 Claims. (Cl. 113-23) Thisinvention relates to sheet metal working machines and particularly towhat is known in the art as a seamer of the type employed in formingdouble seams for attaching heads to the ends of sheet metal barrels ordrums.

Machines for this general purpose are well known in the metal workingart and comprise generally means for holding and rotating a barrel ordrum body and an end member to be joined thereto while forming rollsengage tangentially against the peripheries of the body and end memberto form and flatten the desired double seam. Preliminary to thisseam-forming procedure the edge of the circular end member and the edgeof the cylindrical body member are provided with seam-forming flanges ina manner and according to practices well known in this art.

Heretofore the forming rolls in machines of this class have beencontrolled and moved progressively toward the work as the formingproceeds by mechanical means such as cams or the like. Accordingly, therolls have been advanced toward the work by predetermined increments asthe work is rotated; that is, the forming rolls, each in its turn, moveinwardly toward the work a predetermined distance during each rotationof the work. Since the metal of the drum body and the end member variesin thickness within certain limits and since the conventional doubleseam involves five layers of this metal, such distance controlledrolling produces loose joints when the metal runs thin and results inundesirable strain on the working parts and an undesired cold forming orcold rolling of the metal when it runs thicker than normal.

A primary object of the present invention is to provide rolling meanswherein the feeding arrangement automatically compensates for variationsin the gauge of the metal so that the seams are properly and fullyformed, but without undue strain on the apparatus, regardless of metalthickness variations. Generally speaking, this is accomplished byproviding roll feeding means wherein predetermined pressures are exertedagainst the work by reason of which the forming rolls move against thework during the actual forming and flattening at a greater or less ratewith metals of varying thickness. Since the final pressure of theflattening rolls is constant, uniformly flattened seams are producedeven though the final position of the flattening roll with respect tothe axis of the work varies in accordance with variations in gauge ofthe metal of the work pieces.

The movement of the forming rolls to the work under hydraulic pressurecontrol avoids the necessity for accurate radial positioning of therolls relative to the work axis.

A further object of the invention is to provide novel work strippingmeans for lifting assembled and seamed drum bodies and heads from thecircular chuck against which the seam is rolled and flattened and forcentering the drum head with respect to the seaming chuck by initiallylocating the drum head in a recess in the stripper plate. The presentapparatus provides an arrangement whereby stripper members for differentdiameters of drums may be employed interchangeably by merely lifting onestripper from its operating position and substituting the stripper for adifferent drum diameter. Furthermore, the lifting operation of thestripper member for effecting its stripping function is correlated in anovel manner with a work clamping member which holds the drum body3,d3fl,90fl Patented Apr. 24, 1962 downwardly in proper position for therolling operation. Agam speaking generally, a single fluid pressuresource is alternatively and successively applied to the clamping meansand to the stripping means, whereby operation of a valve to unclamp thework automatically energizes the stripper operating means to effect thestripping function.

A further object of the present invention is the provision of two-stagehydraulic means whereby each forming roll moves from a withdrawnposition to a position in engagement with the work at a rapid rate andunder relatively low hydraulic pressure and progresses through theactual forming movement at a reduced rate and under a substantiallygreater hydraulic pressure, the transition being effected automaticallyby pressure responsive means. The withdrawing movement of each formingroll is effected rapidly under the relatively low hydraulic pressureemployed in the approach movement. This rapid approach of the formingrolls, in addition to promoting the general efficiency of the machine,avoids scraping or skidding of the rolls against the raw metal edges ofthe work pieces during the approach movement.

In a preferred form of the present invention the flattening rollapproaches the work as the curling roll starts its withdrawing movementand the completion of the dwell period of the flattening roll shuts oilthe main motor so that rotation of the work slows and stops While thefiattening roll withdraw-s.

Other objects and advantages of the apparatus of the present inventionwill appear to those skilled in the art from a consideration of thefollowing detailed specification and the accompanying drawing, wherein acomplete embodiment of the principles of the present invention is setforth by way of example. However, it is to be understood that suchembodiment merely exemplifies the principles of the invention and theteachings thereof are not limited thereto or otherwise than as definedin the appended claims.

In the drawings:

FIG. 1 is a general side elevational view of one form of the hydraulicseaming machine of the present invention viewed from the right-hand sidethereof;

FIG. 2 is a vertical cross-sectional view taken centrally through theupper portion of the structure illustrated in FIG. 1 and viewed from theopposite side of the machine from FIG. 1;

FIG. 3 is a top plan view showing the work receiving bed of the machineand the forming rolls, with the superstructure of the machine removedfor added illustration;

FIG. 4 is a fragmentary cross-sectional view of the structure of FIG. 3taken approximately on the line IV1V of FIG. 3;

. FIG. 5 is a cross-sectional view somewhat similar to FIG. 4 but viewedfrom the opposite side of the machine and taken through the firstforming roll and its mounting means, approximately as indicated by theline V--V of FIG. 3;

FIG. 6 is an enlarged fragmentary detailed view of the first formingroll and the work members at the beginning of a forming operation;

FIG. 7 is a view similar to FIG. 6 but showing the completion of thefirst forming operation;

FIG. 8 is a view similar to FIGS. 6 and 7 but showing the second formingroll at the completion, of a squeezing or seam flattening operation;

FIG. 9 is a schematic circuit diagram of the hydraulic system forcontrolling operating movements of the forming rolls; and

FIG. 10 is a View somewhat similar to the right hand portion of FIG. 4but taken obliquely on the line X--X of FIG. 3 and on a somewhat largerscale and showing the stripper plate in the elevated position which itoccupies at the beginning and end of a cycle of operation and betweenoperations.

Like characters of reference denote like parts throughout the severalfigures of the drawings and, referring particularly to FIG. 1, thenumeral designates the bed of the machine and the numeral 11 designatesa column structure or superstructure which is disposed upon and extendsupwardly from the rear side of the bed 10.

A vertical power driven spindle 12 extends upwardly through the bed andcarries at its upper end a work receiving circular chuck member 13 whichwill be referred to in greater detail later herein. In the form of thepresent invention illustrated herein the drive means for spindle 12 isdisposed beneath the floor level and comprises an electric driving motor15 and a speed reducing gear mechanism 16, the output shaft of thelatter extending upwardly for driving connection with the spindle 12 inany desired manner.

The work pieces comprise a sheet metal cylindrical drum body and acircular head or bottom member 21, these parts being shown particularlyin FIGS. 4, 6, 7 and 8. The present apparatus shows a head or bottommember 21 being secured to one end of a cylindrical drum 20, it beingunderstood however that heads 21 may be secured to both ends of drum 20by successive operations if that be desired.

Referring particularly to FIG. 6, drum 20 is provided with an outwardannular flange 22 and head member 21 is provided with a downward annularflange 23 and an outward terminal flange 24, the flanges 22, 23 and 24being preliminarily formed on the parts 20 and 21 in any desired manner.

As shown in FIG. 4, spindle 12 has anti-friction bearing in bed 10 as at25 and 26 and carries at its upper end a chuck member 13 referred topreviously herein which comprises merely a circular structure of suchdiameter that the flanged head member 21 may be placed thereover andlocated centrally thereby as shown in FIGS. 4 and 6. Following suchplacement of the head member 21 on chuck member 13 the cylindrical drumbody member 20 is placed thereover likewise as shown in FIGS. 4 and 6and a clamp plate 28 is brought downwardly against the upper end of drum20 to hold the same against axial displacement from the position shownin FIGS. 4 and 6.

The clamp member 28 and its supporting and operating instrumentalitiesare illustrated in detail in FIG. 2, to which reference will now be had.

Clamp plate 28 is carried for free relative rotation at the lower end ofa spindle 31; which in turn is carried for free vertical movement in abearing 31 fixed to the outer end of an outboard bearing supportstructure 32 which is mounted against the front face of column 11 forrelative vertical adjusting movement. Axial thrust antifriction bearingmeans 34 is provided to mount the clamp plate 28 for free rotationrelative to spindle and vertical movements of spindle 30 relative tohearing 31 are effected and controlled by a fluid pressure cylinder andpiston arrangement 36, the operating piston rod of which is designated37 in FIG. 2.

Outboard bearing support structure 32 includes a mounting plate portion40 which is guided for vertical movement by ways or guides 41 fixed tothe front of column member 11. A nut member 42 is fixed to the rear faceof plate 40 and engages a screw 44 which is rotatably mounted at itsupper and lower ends in bearings 45 and 46 carried by column 11.

The upper end of screw 44 has gear connection with power drive means inthe form of an air motor designated generally by the numeral 47 anddriving operation of the motor 47 in opposite directions raises andlowers support 32 and the clamp plate structure carried thereby, suchadjustments being made to establish a proper working height of thebearing support structure for drums of various lengths. Secondaryvertical movement of clamp '4 plate 28 by operation of the piston andcylinder mechanism 36 is used to clamp and unclamp plate 23 with respectto a given drum workpiece between successive seaming operations.

Operating air pressure is directed to the upper and lower ends ofcylinder 36 by conduits 43 and 49 fixed to bearing support 32 which inturn receive air pressure from a conduit junction block 51 fixed tocolumn 11. The numeral 50 in FIG. 2 designates a flow control valve inconduit 49 which determines the speed of operation of the clampingmechanism. Communication between block 51 and the conduits 48 and 49 isby way of a pair of flexible conduits 52 which extends over pulleys 53rotatably mounted upon a block 54 fixed to column 11. A pair of slacktake-up pulleys 55 engage the conduits 52 between block 51 and pulleys53 and are weighted as at 56 to take up the varying slack of theconduits occasioned by up and down movements of the outboard bearingsupport 3 2.

Control of operating air pressure to opposite ends of the cylinder 36 byway of conduits 48 and 49 is effected manually by means of a four-wayvalve 60 which is operable alternatively to supply operating airpressure to either of the conduits 48 or 49. When operating air pressureis applied to conduit 49 for raising or unclamping movement of plate 28the same valve setting applies operating air pressure, by means of aconduit indicated schematically at 57 in FIG. 2, to a work stripperoperating mechanism, presently to be described.

Reference will now be had to the forming rolls, which form and securethe double seam which joins the drum 20 with the head or bottom member21, and the supporting and positioning means for such forming rolls.Referring particularly to FIG. 5, a generally fiat box-like member ismounted between the upper portions of the side walls of base 10 forguided horizontal movement from left to right as viewed in FIGS. 3, 4and 5. Such guided horizontal movement of the box-like member 65 is forthe purpose of variably positioning the entire forming roll structure asa unit to accommodate the same to the forming of seams on drums andheads of varying diameters.

Securely adjusted positioning of the member 65 is effected by means of ascrew 66 which is journaled in a bearing 67 fixed to base 10 and heldagainst axial movement. Rotation of screw 66 is by means of a handle 67including a detent pin 68 for locking the screw 66 in various positionsof adjustment. Screw 66 passes through an internally threaded nut member69 which is fixed to the underside of box-like member 65. A pointer 70carried by the box-like member moves relative to a scale 71 fixed tobase 10 to indicate directly the drum diameter for which the box-likemember 65 is positioned.

A pair of forming roll carriers 72 and 73 are positioned within thebox-like member 65 in side-by-side relation, each being guided forindependent horizontal movement in the box-like member 65, also fromleft to right as viewed in FIGS. 3, 4 and 5. The carriers 72 and 73 areattached at one end of each to piston rods 74 and 75 which project frompistons contained in fluid pressure operating cylinders 76 and 77 and inthe present instance the operation is by means of hydraulic fluid.

At its opposite end each of the carriers 72 and 73 gives rotatablesupport to one of the forming rolls. In FIG. 5 carrier 72 supports aforming roll 80 which curls the flanges into interlocking relationshipprior to the final flattening of the seam formed thereby. Forming roll80 is mounted upon a shaft 81, preferably by means of antifrictionbearings (not shown) contained within the roll, so that the roll 80rotates freely on supporting shaft 81.

Shaft 81 is threaded at its lower end into a portion of carrier 72 asclearly shown at 82 in FIG. 5 and roll 80 is held against relative axialmovement on shaft 81. Accordingly, shaft 81 may be adjusted upwardly anddownwardly by the threaded connection of its lower end to position theroll 80 accurately in a vertical direction. As

shown in FIG. 3, such vertical adjustment of roll 80 is maintained by aspring biased locking or detent pin 84 which engages notches formedabout the periphery of a locking wheel 85 which is fixed to shaft 81.

A flattening roll 88 is similary mounted upon the other carrier 73, thesame reference characters being applied to the various supporting,adjusting and operating parts thereof as in the case of the forming roll80.

It is to be understood that the forming rolls, that is the curl formingroll 80 and the flattening roll 88, are entirely conventional in theirperipheral formations and that the novelty herein resides, insofar asthe forming rolls are concerned, in the manner in which they areoperated, positioned, adjusted and controlled. It is accordinglysufficient to state that roll 80 contains two curl forming grooves, oneof which is shown at the beginning of a curling operation in FIG. 6 andat the conclusion of a curling operation in FIG. 7. The double groovearrangement permits the rolls to be reversed, top to bottom, to presenta new groove when the first groove becomes worn, thus doubling the lifeof each forming roll.

Flattening roll 88 is similarly provided with two flattening grooves,one of which is shown at the conclusion of a flattening operation inFIG. 8. It is further to be understood that rolls 80 and 88 moveprogressively toward the work as their forming and flattening operationsproceed, such movements in prior art devices having generally been byway of mechanical cams which produce predetermined increments of feedingmovement toward the work for each rotation of the drum and head members.

Reference will now be had to novel stripping means for lifting theseamed drum and head or bottom member from the chuck member 13 at theconclusion of a seamforming and flattening sequence of operations. Itwill be understood that these operations, particularly the finalflattening operation, causes the drum head or bottom member 21 to fitquite closely about the chuck member 13 so that lifting of the finishedassembly from the chuck member requires a substantial upward force.

The present apparatus provides stripper members and mounting means whichare so arranged that the stripper members are readily interchangeable toaccommodate the manufacture of drums of various diameters and alsoprovides for correlated operation with the air-pressureoperated topclamp member 28 so that the work is automatically stripped from thechuck member in conjunction with the unclamping movement of member 28.Further: more, in the present apparatus the stripper member initiallypositions the drum head and locates the same centrally with respect tothe chuck member 13.

Having reference particularly to FIG. 3, the stripper element itself, inthe present instance, comprises a generally C-shaped flat plate memberdesignated 100. The inside diameter of plate member 100 is such that itjust clears the outer diameter of chuck member 13 and the upper surfaceof the plate member 100 is recessed at its inner portion to form anarcuate ledge designated 102. in FIGS. 3, 4 and 1 0. Stripper member 100is bored to receive a pair of guide pins 101 which are secured at theirlower ends to the work surface of bed and project upwardly therefrom asclearly shown in FIG. 3.

Stripper member 106 rests upon the upper ends of four piston rods 104which project upwardly from fiuid pressure operating cylinders 105 whichare likewise attached to the work surface of base 10. In FIG. 4 thepiston rods are in their lower positions wherein they support strippermember 100 at a position slightly below the flanges 22 and 24 of thework pieces to permit unobstructed operation of the forming Dolls 80 and88.

When valve 60 is operated to reverse the application of pressure tocylinder 36 and raise piston rod 37 and clamp plate 38, operatingpressure is automatically and simultaneously applied beneath the pistonsof piston rods 104 to project the latter upwardly and raise stripper 100to force the lower end of the finished work members from chuck 6 member13. The air pressure conduit from valve 60 to the cylinders 195 isindicated schematically at 107 in FIG. 2 and in FIG. 10. In the absenceof air pressure piston rods 104!- are urged to a lower withdrawnposition by springs 16% in the cylinders 105 as shown in FIG. 10.

Referring more particularly to FIG. 10, after a stripping operation anduntil a succeeding clamping operation the stripper member 10% remains inthe elevated position shown in FIG. 10. At the beginning of a cycle ofoperation a flanged head member 21 is placed on stripper member 1% andits peripheral flange Z4 is located by ledge 102. Application ofclamping pressure lowers the stripper member 100 and the head member ismoved down over chuck member 13.

Reference will now be had to the hydraulic system for operating andcontrolling the movements of the forming rolls 8d and 38 and in thisconnection reference will be had particularly to the hydraulic circuitdiagram, FIG. 9. Hydraulic pressure is supplied by a conventional doublepump mechanism which is of a known type, wherein the combined deliveryof a large pump and a small pump is delivered to the output line belowspecified pressures and the large pump bypasses to the reservoir 121above certain pressures whereupon the small pump continues to deliverfluid at a substantially less quantity but at a relatively highpressure.

A pair of four-Way valves 123 and 124 are of the spring centered typeand thus normally fluid from the pump mechanism 120 flows through theconduit 125 through valve 123, through a conduit 126, through valve 124,and back to the pump reservoir through a conduit 127. The numeral 128designates a check valve which imposes a back pressure of suflicientdegree to actuate the internal pilot operation which is conventional infour-way valves of the type employed in the case of valves 123 and 124.

The four-way valves 123 and 124 are each adapted to be operated inopposite directions by pairs of solenoids 131 and 132 and 133 and 134,respectively. At the beginning of the cycle solenoid 134 is energized.This directs the combined delivery of both pumps into the head end ofcylinder '76 through a line 135. The forming roll 3t) thus moves to thework at a relatively rapid speed. As soon as pressure in line I135builds up in excess of the unloading valve of pump mechanism 120, thelow pressure pump thereof unloads and the balance of the forwardmovement of forming roll 8% is accomplished at high pressure by thesmall pump only. A relief valve 136 in line 135 determines the maximumpressure to cylinder 76.

A pressure switch 137 is in communication with line 135 and whenpressure has built up to the setting of this pressure switch a timer(not shown) is started for a dwell period. When this dwell expiressolenoid 1'34 is deenergized and solenoid 133 is energized. Thisreverses the setting of four-way valve 124 and pump delivery is thenceto the line 138 leading to the opposite end of cylinder 7e, whereuponthe forming roll St? is returned under the combined operation of bothpumps and at a relatively rapid speed.

In FIG. 9 the numerals 139 and 140 designate a pair of limit switcheswhich are arranged to be contacted by the respective roll carriers asthe latter move to their return positions. When forming roll 80 is fullyretracted limit switch 13% is engaged and this de-energizes solenoid133. When the dwell period established by timer 137 expires, solenoid132 becomes energized and the combined delivery of both pumps is nowdirected into the head end of the cylinder 77 of the flattening roll 83through line 141 to effect rapid advance of roll 88. When the work iscontacted pressure will build up in line 141 as previously described andthe balance of the flattening work will be accomplished by the smallhigh pressure pump only.

A further pressure actuated switch 142 is in communication with line 141and when pressure builds up in the latter to a predetermined point afurther timer (not shown) begins a dwell period. When the dwell expiressolenoid 132 is de-energized and solenoid 131 is energized. Combinedpump delivery is now directed to the left-hand end of cylinder 77 by wayof a line 143 to effect rapid return of forming roll 88. Upon fullreturn limit switch 140 is contacted which de-energizes solenoid 131 toput the hydraulic system in neutral with both of the valves 123 and 124centered as before. When the dwell period of the timer expires, the mainmotor 15 is deenergized, so that it slows down and stops while theforming roll 88 is withdrawing.

In a full cycle of operation the operator loads the work pieces into themachine and operates valve 60 to cause clamping operation of cylinder36. After the work is clamped the operator actuates a start button formain motor 15 which rotates the clamped workpiece. A timing relay (notshown) operates from the start button of the main motor to energizesolenoid 134 and institute a cycle of hydraulic operation as previouslydecribed. Following the stopping of the main motor at the conclusion ofa hydraulic cycle of operation and with the hydraulic system in neutral,the operator reverses valve 60 to release the clamp and strip the workas described previously herein.

We claim:

1. Sheet metal forming apparatus for joining an end member to a drumbody comprising, a bed and means thereon for supporting such end memberand for rotating the same on its axis, clamp means engageable against anend of a drum body to hold the opposite end thereof in coaxial abuttingengagement with said end member, forming rollers movable peripherallyagainst the abutting portions of the end member and the drum body toform a seam therebetween, vertical guide means extending upwardly fromsaid bed, and a plurality of push rods projecting upwardly from saidbed, interchangeable stripping means generally surrounding said supportmeans, said stripping means having vertical sliding engagement with saidguide means and being adapted to rest upon said push rods, reciprocatingfluid motor means for moving said clamp means to and from clampingposition, and fluid motor means operable jointly with movement of saidrecopricating fluid means to unclarnping position for raising said pushrods and thus moving said stripping means against the end member anddrum body to strip the same from said support means.

2. Sheet metal forming apparatus for joining an end member to a drumbody comprising, a bed and means thereon for supporting such end memberand drum body and for rotating the same on the axis of the drum body,forming rollers movable peripherally against the abutting portions ofthe end member and the drum body to form a seam therebetween, verticalguide means extending upwardly from said bed, and a plurality of pushrods spaced laterally from said guide means and projecting upwardly fromsaid bed, interchangeable stripping means having vertical slidingengagement with said guide means and being adapted to rest upon saidpush rods and fluid motor means for raising said push rods to move saidstripping means against the end member and drum body to strip the samefrom said support means.

3. Sheet metal forming apparatus for joining an end member to a drumbody comprising, a bed and means thereon for supporting such end memberand for rotating the same on its axis, clamp means engageable against anend of a drum body to hold the opposite end thereof in coaxial abuttingengagement with said end member, forming rollers movable peripherallyagainst the abutting portions of the end member and the drum body toform a seam therebetween, vertical guide means extending upwardly fromsaid bed, and a plurality of push rods projecting upwardly from saidbed, interchangeable stripping means generally surrounding said supportmeans, said stripping means having vertical sliding engagement with saidguide means and being adapted to rest upon said push rods, andreciprocating fluid motor means raising said push rods to move saidstripping means against the end member and drum body to strip the samefrom said support means.

4. Sheet metal forming apparatus for joining an end member to a drumbody comprising, a bed and means thereon for supporting such end memberand for rotating the same on its axis, clamp means engageable against anend of a drum body to hold the opposite end thereof in coaxial abuttingengagement with said end member, forming rollers movable peripherallyagainst the abutting portions of the end member and the drum body toform a seam therebetween, vertical guide means extending upwardly fromsaid bed, and a plurality of push rods projecting upwardly from saidbed, interchangeable stripping means generally surrounding said supportmeans, said stripping means having vertical sliding engagement with saidguide means and being adapted to rest upon said push rods, andreciprocating fluid motor means for raising said push rods to move saidstripping means against the end member and drum body to strip the samefrom said support means, said stripping means having an arcuate recessconcentric with the axis of drum rotation adapted to receive and locatean end member when the stripping means is in raised position.

5. Sheet metal forming apparatus for joining an end member to a drumbody comprising, a bed and means thereon for supporting such end memberand for rotating the same on its axis, clamp means engageable against anend of a drum body to hold the opposite end thereof in coaxial abuttingengagement with said end member, means engaging the abutting portions ofthe end member and the drum body to form a seam therebetween, strippingmeans generally surrounding said support means, and means raising saidstripping means against the end member and drum body to strip the samefrom said support means, said stripping means having an arcuate recessconcentric with the axis of drum rotation adapted to receive and locatean end member when the stripping means is in raised position.

References Cited in the file of this patent UNITED STATES PATENTS1,275,867 Davis Aug. 13, 1918 1,982,711 Vickers Dec. 4, 1934 2,228,651Buck Jan. 14, 1941 2,307,544 Robinson Jan. 5, 1943 2,516,322 JacokesJuly 25, 1950 2,559,125 Lee July 3, 1951 2,779,301 Grotnes Ian. 29, 19572,805,635 Hale Sept. 10, 1957 2,845,887 Kradoska Aug. 5, 1958

